Fixation with Carnoy's fluid reduces the number of chymase-positive mast cells: Not all chymase-positive mast cells are also positive for tryptase

Mast cells in the nasal mucosa can be studied by means of monoclonal antibodies (mAb) against tryptase (T(+)MC) and chymase (C(+)MC). Fixation with acetone gives more positive cells than does fixation with Carnoy's fluid. In frozen biopsy specimens of allergic nasal mucosa fixed with acetone, the number of T(+)MC equals that of C(+)MC. When fixed with Carnoy's fluid, however, the number of T(+)MC is larger than the number of C(+)MC. The decrease in both T(+)MC and C(+)MC resulting from fixation with Carnoy's fluid is time-related and depends on the type of mAb used. Carnoy fixation time gives a decrease in the number of C(+)MC within 1 min, whereas the number of T(+)MC decreases only after 10 min. Within 1 min, the number of C(+)MC decreases to a level where continued fixation no longer gives further decreases in the number of cells. Two populations of mast cells can be distinguished here: one sensitive and the other insensitive to Carnoy's fluid. When double-staining is used, fixation with acetone gives three populations of mast cells: one positive for tryptase (T(+)C(-)MC), another positive for tryptase and chymase (T(+)C(+)MC), and a third one positive for chymase (T(-)C(+)MC). These three populations were found in lymph node, spleen, thymus, dermis, lung parenchyma, small intestinal submucosa, and nasal mucosa.